GB2568105A

GB2568105A - A joined article, a method of de-bonding an article and a method of curing a binder

Info

Publication number: GB2568105A
Application number: GB1718388.0A
Authority: GB
Inventors: Xin Charles Ng Wu; Vadugappatty Srinivasan Dharun
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 2017-11-07
Filing date: 2017-11-07
Publication date: 2019-05-08
Also published as: GB201718388D0

Abstract

There is disclosed a joined article 10 comprising opposing substrates 12, a binder 14 between the substrates 12 binding the substrates 12 together and a de-bonding membrane 20 embedded within the binder 14 and configured to selectively expand to enable de-bonding of the substrates 12. The de-bonding membrane 20 comprises a carrier 22 comprising nano-fibres, wherein the carrier 22 is impregnated with an expandable agent 24 which expands in response to heating. Preferably, the nano-fibre is comprised of a single or plurality of electro-spun nano-fibres. Preferably the expanding agent comprises graphite There is also disclosed a method of de-bonding a joined article 10 comprising opposing substrates 12, a binder 14 between the opposing substrates 12 and a de-bonding membrane 20 embedded within the binder 14 having a carrier 22 impregnated with an expandable agent 24. Preferably, the carrier is heat by inducing current into the carrier. The method comprises heating the carrier 22 such that the expandable agent 24 expands and de-bonds the opposing substrates 12. There is further disclosed a method of curing an adhesive 14, 114 comprising embedding a membrane 20, 120 in an adhesive 14, 114 and heating the membrane 20, 120 so that heat transfers from the membrane 20, 120 to the adhesive 14, 114 to cure the adhesive 14, 114.

Description

A JOINED ARTICLE, A METHOD OF DE-BONDING AN ARTICLE AND A METHOD OF CURING A BINDER

The present invention relates to a joined article, a method of de-bonding an article and a method of curing a binder.

It is known to bond parts to form an article. Examples include lightweight structures for use in the aerospace industry comprising fibre-reinforced composite parts which are joined together using adhesives to form a joined article. Such articles or the joined parts may become damaged or need to be repaired in use. If only some of the individual parts are damaged, it may be desirable to de-bond the parts to salvage the undamaged parts.

According to a first aspect, there is provided a joined article comprising: opposing substrates; a binder between the substrates binding the substrates together; and a debonding membrane embedded within the binder and configured to selectively expand to enable de-bonding of the substrates, the de-bonding membrane comprising a carrier comprising nano-fibers; wherein the carrier is impregnated with an expandable agent which expands in response to heating.

The de-bonding membrane may comprise electro-spun nano-fibre. The de-bonding membrane may comprise a single electro-spun nano-fibre.

The expandable agent may expand in response to heating. The carrier may be selectively heated to heat the binder. The carrier may be arranged to enable selective heating of the carrier to heat the binder. The carrier may be electrically conductive and may be thermally responsive to current for selective heating. The carrier may be thermally responsive to induced current.

Induced currents may create eddy currents in the carrier which dissipate heat and therefore heat the carrier.

The carrier may comprise nylon nano-fibres coated with electrically conductive particles. The conductive particles may be silver particles. The conductive particles may be iron oxide particles coating the nano-fibres.

The expandable agent may be configured such that expansion of the expandable agent is discontinuously responsive to heating. Expansion of the expandable agent may have a sigmoidal relationship with heating. The expandable agent may be activated by heating beyond a threshold temperature. In other words, the expandable agent may remain in an unexpanded state when the temperature is below a threshold temperature and may expand when the temperature rises above the threshold temperature (e.g. suddenly or discontinuously expand over a limited temperature range above the threshold).

The expandable agent may comprise thermally expandable microspheres. The term “thermally expandable microspheres” has an accepted meaning in the art, indicating a small shell containing a fluid. The fluid expands within the shell (for example owing to heating to boiling point) to cause expansion of the shell. The shell may be thermally responsive to resist expansion below a threshold, and soften to permit expansion above the threshold. The expandable agent may comprise a blowing agent (otherwise known as a foaming agent), for example a physical blowing agent or a chemical blowing agent, each having accepted meanings in the art. The blowing agent may be provided in an expandable structure. The expandable agent may comprise thermally expandable microspheres comprising physical or chemical blowing agents (also known as foaming agents). The expandable agent may be an expandable graphite intercalation compound (GIC), for example particulate acid intercalated graphite.

According to a second aspect, there is provided a method of de-bonding an article comprising opposing substrates, a binder between the opposing substrates and a debonding membrane embedded within the binder having a carrier impregnated with an expandable agent, the method comprising: heating the carrier such that the expandable agent expands and de-bonds the opposing substrates.

The carrier may be heated by inducing a current in the carrier. The article may be in accordance with the first aspect.

According to a third aspect, there is provided a method of curing a binder (such as an adhesive) comprising: embedding a membrane in adhesive binder; and heating the membrane so that heat transfers from the membrane to the binder to cure the binder.

The membrane may be heated by inducing a current in the membrane.

The membrane may be a de-bonding membrane comprising a carrier and an expandable agent, wherein the heating to cure the binder may be such that the expandable agent remains in an unexpanded state, the method may further comprise subsequently heating the carrier so that the expandable agent is heated beyond a threshold temperature to cause expansion of the expandable agent for de-bonding the article.

The article may be in accordance with the first aspect.

The invention may comprise any combination of features and/or limitations referred to herein, except combinations of such features as are mutually exclusive.

Embodiments will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 schematically shows a joined article comprising a de-bonding membrane;

Figure 2 is a flow chart showing the steps of a method of de-bonding a joined article such as shown in Figure 1.

Figure 3 schematically shows a membrane embedded within a binder;

Figure 4 is a flow chart showing the steps of a method of curing adhesive binder; and

Figure 1 shows a joined article 10 comprising two opposing substrates 12, which are joined together by a binder, in particular a cured adhesive 14. In this example, the substrates 12 are carbon fibre reinforced plastic (CFRP) components and the adhesive 14 is epoxy. However, in other examples the substrates may comprise any materials which are to be joined together, and the adhesive may be any suitable binder.

A de-bonding membrane 20 is embedded within the epoxy adhesive 14. The debonding membrane 20 comprises a carrier 22 and an expandable agent 24. The debonding membrane 20 is for de-bonding the substrates 12 to permit separation of the substrates, thereby inhibiting damaging the substrates 12.

The carrier 22 is impregnated with the expandable agent 24. For example, the carrier may be impregnated with the expandable agent by coating the nano-fibers of the carrier 22 with the expandable agent 24, or otherwise treating the carrier 22 so that the expandable agent 24 is interspersed between nano-fibers. For example, the expandable agent 24 may be applied to the carrier 22 by immersing the expandable agent in a bath of expandable agent 24 or spraying the carrier 22 with expandable agent.

The expandable agent 24 is configured to expand in response to heating. In this example, the expandable agent 24 comprises particles of acid intercalated graphite which expand when they are heated (i.e. in response to a change in temperature, or upon reaching a threshold temperature). In other examples, other expandable agents may be used, for example thermally expandable microspheres, which may comprise a physical foaming agent (such as liquid solvents including toluene) or a chemical foaming agent (such as azo and diazo compounds).

The carrier 22 comprises nano-fibres. The term nano-fibres is an industry standard term to be interpreted to mean fibres having a diameter of 100nm or less. In this example, the carrier 22 comprises a continuous nylon electrospun nano-fibre which has been formed into a generally planar mesh. In this particular example, the carrier 22 comprises a single fibre. However, in other examples, the carrier may comprise more than one electrospun nano-fibre, or the fibres could be manufactured by any other suitable means. The nano-fibres could be made of any suitable material, such as Kevlar™ or glass fibre reinforce polymer (GFRP). In this example, the carrier 22 is fully embedded within the adhesive 14 such that every side of the carrier is in contact with the adhesive. In other words, the carrier 22 is surrounded by, or enveloped by, the adhesive 14.

Electrically conductive particles are embedded in the nano-fibre mesh so that the carrier 22 (i.e. the nano-fibre mesh in combination with the electrically conductive particles) is electrically conductive. In this particular example, silver particles are embedded in the nylon nano-fibre mesh.

The carrier 22 can be selectively heated to cause expansion of the graphite particles 24. The carrier 22 is thermally responsive to current. In this example, the carrier 22 can be heated by inducing a current in the carrier 22. However, in other examples, the carrier may be heated by applying a current to generate resistive heating in the carrier.

The expansion of acid intercalated graphite particles 24 has a discontinuous relationship with the temperature of the particles 24. In other words, the acid intercalated graphite particles 24 remain generally in an unexpanded state below a threshold temperature but suddenly expand when the temperature of the graphite particles 24 exceeds the threshold temperature. The expansion of the graphite particles 24 follows a generally sigmoidal relationship beyond the threshold temperature so that expansion is gradual just above the threshold temperature and rapidly increases as temperature increases, before it tapers off and plateaus at yet higher temperatures. The particles may retract again above a certain temperature after the expansion has plateaued.

Figure 2 is a flow chart of a method of de-bonding a joined article 200 which will be described by way of example with reference to the joined article 10 described above with reference to Figure 1.

In block 202 of the method, the de-bonding membrane 20 is heated by heating the carrier 22. In this example, the carrier 22 is heated by applying an electric current to the carrier 22. In particular, the electric current is induced in the carrier 22 by changing a magnetic field in the carrier 22. The changing magnetic field induces eddy currents in the carrier 22 which dissipate heat, thereby heating the carrier 22. For example, the eddy currents may be induced by application of an AC electromagnet around or adjacent the article 10. In other examples a current may be directly applied to opposing ends of a carrier such that the carrier is heated by resistive heating.

The heat induced within the membrane 120 is transferred through the surrounding adhesive 14 to the graphite particles 24.

Current is induced in the carrier 22 until the temperature of the graphite particles 24 exceeds the threshold temperature at which the graphite particles 24 begin to expand. Due to the discontinuous relationship of the expansion and temperature of the graphite particles 24, when the graphite particles 24 are heated by the carrier 22, they remain in an unexpanded state until the threshold temperature is reached. When the temperature of the graphite particles 24 reaches, and then exceeds the threshold temperature, the graphite particles 24 suddenly begin to expand to causing cracking (i.e. rupture) of the adhesive 14. In this example the threshold temperature is approximately 80 degrees centigrade. In other examples, the graphite particles may be configured so that the threshold temperature is higher or lower than 80 degrees centigrade.

In block 204, the substrates 12 are separated by the application of mechanical force pulling them apart. The cracks in the adhesive 14 weaken the adhesive so that it is possible to mechanically separate the substrates 12 with reduced forces (as compared with un-weakened adhesive prior to expansion of the particles 24) so that the risk of damaging the substrates 12 during separation is reduced.

Further, since the carrier 22 is embedded within the adhesive, when it is heated, the heat is transferred from the carrier 22 to the graphite particles 24 and the surrounding adhesive 14. However, the applicant has found that heating the carrier generates a temperature gradient in the article 10 from the carrier 22, such that it takes the heat longer to transfer through the adhesive 14 to either of the substrates 12 than to the graphite particles 24 (in other words, the carrier 22 and expandable agent are at higher temperatures than the adjacent portions of the substrates 12 during heating of the carrier 22). Accordingly, the graphite particles 24 will begin to expand before the heat transferring from the carrier 22 damages the substrates 12.

Figure 3 shows a second example article 100 comprising a membrane 120 which is embedded within a binder, in particular a cured adhesive 114. The membrane 120 in this example is equivalent to the carrier 22 of the joined article 10 of Figure 1, albeit with no expandable agent in this example. As such, the membrane 120 comprises a single electrospun nylon nano-fibre embedded with electrically conductive particles, in particular silver particles. However, in other examples the membrane may comprise more than one nano-fibre, and may comprise any suitable electrically conductive particles.

The binder in this example is an epoxy resin. However, the binder can be any suitable binder. The binder may be selected from a set of binders or adhesives for which a rate of curing increases with higher temperatures.

The membrane 120 is used to aid and control curing of the adhesive in this example as described with reference to Figure 3 below.

Figure 4 shows a flow chart with steps of a method 400 of curing a binder 114 to join opposing parts to provide a joined article such as the article 100 shown in Figure 3.

In block 402 a membrane 120 is formed from an electrospun nylon nano-fibre embedded with an expandable agent, in particular silver particles. In this example, the membrane 120 is formed into a generally planar porous mesh, although in other examples the membrane can be formed into any suitable shape for curing an adhesive. Block 404 comprises subsequently embedding the membrane 120 within an adhesive 114, which in this example is an epoxy resin. Since the membrane 120 is a porous mesh, the membrane 120 becomes fully immersed (or embedded) in the adhesive 114. Block 406 comprises subsequently heating the membrane 120 to cure the adhesive.

The membrane 120 is heated by applying an electric current to the membrane 120. In this example, the electric current is applied by inducing a current in the membrane 120 by changing the magnetic field in the membrane 120. This changing magnetic field forms eddy currents in the membrane 120 which dissipate heat, thereby heating the membrane 120.

The heat induced within the membrane 120 is transferred to the surrounding adhesive 114, so that the adhesive 114 begins to cure. In this example, current is induced in the membrane 120 until the adhesive 114 is cured.

The amount of current induced in the membrane can be controlled to cure the adhesive 114 at a desired rate.

If the adhesive 114 is bonding two substrates together, such as shown in Figure 1, the heat from the membrane 120 would have to transfer through the adhesive 114 before reaching either substrate. Accordingly, using the membrane 120 to cure the adhesive 114 can reduce the risk of damage to substrates which are being bonded together, as it enables local heating at the membrane with a temperature gradient of relatively reduced temperature at surrounding portions of the parts that form the joined article.

The joined article 100 of Figure 1 may also be manufactured using the method described above reference to Figure 4. In such an example method of manufacture, the de-bonding membrane 20 comprising the carrier 22 and the expandable agent 24 replaces the membrane 120 in blocks 402 and 404. In such a modified example, in block 402 the de-bonding membrane 20 is formed by forming the carrier 22 in the same manner as the membrane 120 and coating the carrier 22 with intercalated graphite particles 24 to form the de-bonding membrane 20 as described above.

In block 406 the de-bonding membrane 20 is heated to cure the adhesive as described above.

The example modified method further includes laying up the substrates 12 and the adhesive 14 with the embedded de-bonding membrane 20 before heating the carrier 22 to cure the adhesive 14.

In this example, in order to cure the adhesive with the de-bonding membrane 20 comprising the expandable agent 24, the induced current is controlled so that the temperature of the expandable agent 24 does not exceed the threshold temperature at which the expandable agent 24 expands. The threshold temperature is only exceeded when it is required to separate the substrates by de-bonding.

Embedding a de-bonding membrane within an adhesive can reduce desirable characteristics of an adhesive, such as the strength, or fracture toughness. However, it has been found that embedding a nylon nano-fibre carrier within the epoxy results in a joint with a higher fracture toughness than using the adhesive alone.

Although it has been described that the nano-fibres are made of nylon and are embedded with silver particles, in other examples, the nano-fibres could be made of any suitable material. Further, the nano-fibres may be embedded with particles of any electrically conductive material, in order to make the nano-fibres electrically conductive, or the nano-fibres could be made of an electrically conductive material so that embedding conductive particles in the nano-fibre is not necessary. In yet further examples, the nano-fibres may not be electrically conductive at all.

CLAIMS:

Claims

CLAIMS:

1. A joined article (10) comprising:

opposing substrates (12);

a binder (14) between the substrates (12) binding the substrates together; and a de-bonding membrane (20) embedded within the binder (14) and configured to selectively expand to enable de-bonding of the substrates (12), the de-bonding membrane (20) comprising a carrier (22) comprising nano-fibers;

wherein the carrier (22) is impregnated with an expandable agent (24) which expands in response to heating.

2. A joined article (10) according to claim 1, wherein the de-bonding membrane (20) comprises electro-spun nano-fibre.

3. A joined article (10) according to claim 2, wherein the de-bonding membrane (20) comprises a single electro-spun nano-fibre.

4. A joined article (10) according to any preceding claim, wherein the carrier (22) can be selectively heated to heat the binder.

5. A joined article (10) according to claim 4, wherein the carrier (22) is electrically conductive and is thermally responsive to current for selective heating.

6. A joined article (10) according to claim 5, wherein the carrier (22) is thermally responsive to induced current.

7. A joined article (10) according to any preceding claim, wherein the expandable (24) agent is configured such that expansion of the expandable agent (24) is discontinuously responsive to heating.

8. A joined article (10) according to any preceding claim, wherein the expandable agent (24) is activated by heating beyond a threshold.

9. A joined article (10) according to any preceding claim, wherein the expandable agent (24) is particulate acid intercalated graphite.

10. A method of de-bonding an article (10) comprising opposing substrates (12), a binder (14) between the opposing substrates and a de-bonding membrane (20) embedded within the binder having a carrier (22) impregnated with an expandable agent (24), the method comprising:

heating the carrier (22) such that the expandable agent (24) expands and debonds the opposing substrates (12).

11. A method according to claim 10, wherein the carrier (22) is heated by inducing a current in the carrier.

12. A method of curing adhesive (14, 114) comprising:

embedding a membrane (20, 120) in an adhesive (14, 114); and heating the membrane (20, 120) so that heat transfers from the membrane to the adhesive to cure the adhesive (14, 114).

13. A method according to claim 12, wherein the membrane (20, 120) is heated by inducing a current in the membrane.

14. A method according to claims 12 or 13, wherein the membrane (20) is a debonding membrane comprising a carrier (22) and an expandable agent (24), wherein the heating to cure the adhesive (14) is such that the expandable agent (24) remains in an unexpanded state, the method further comprising subsequently heating the carrier (22) so that the expandable agent (24) is heated beyond a threshold temperature to cause expansion of the expandable agent (24) to enable de-bonding.

15. A method of curing an adhesive according to claim 14, wherein the expandable agent (24) is particulate acid intercalated graphite.

Intellectual Property Office

Application No: GB1718388.0

Claims searched: 1-11

Examiner:

Mr James Tagg

Date of search: 8 May 2018

Patents Act 1977: Search Report under Section 17

Documents considered to be relevant:

Category Relevant to claims Identity of document and passage or figure of particular relevance X,Y X: 1-8 & 10; Y: 9 & 11 W02004/087826 A (DEBONDING LTD) See Whole Document. Y 9 US2010/323202 A (SIKA TECHNOLOGY) See Paragraph [0004], Y 11 WO00/40648 A (MINNESOTA MINING & MFG) See pg. 6 lines 8-12 & pg. 10, line 29 - pg. 11, line 9.